How Does The Acid Get Into The Stomach?
Hydrochloric acid is secreted by special cells in the stomach wall. There is always some amount of acid being produced, but acid pumps really produce when food enters the stomach. Hydrochloric acid prepares food for digestion, especially proteins.
Hydrochloric acid activates pepsinogen into the enzyme pepsin. Normally proteins exist in a tightly coiled globular structure; acids denature dietary protein which then results in the protein unraveling into a more linear structure. This then allows enzymes access to the peptide bonds so the protein can be broken down later after the food is in the small intestine.
The resulting highly acidic environment in the stomach lumen causes proteins from food to lose their characteristic folded structure (or denature). This exposes the protein’s peptide bonds. The chief cells of the stomach secrete enzymes for protein breakdown (inactive pepsinogen and rennin). Hydrochloric acid activates pepsinogen into the enzyme pepsin, which then helps digestion by breaking the bonds linking amino acids, a process known as proteolysis. In addition, many microorganisms have their grwth inhibited by such an acidic environment, which is helpful to prevent infection.
Hydrochloric acid prepares pepsin and bile activity. Above pH of 4.0, stomach enzymes and bile acids are inactive. Once stomach acid lowers pH to less than 4.0, pepsin and bile acids becomes active. This is why those on acid reflux medications often get sicker over time. In the beginning, symptoms of reflux lessen but their overall health and digestion becomes less than optimal, and some patients will start to exhibit a disease state.
In The duodenum / Small Intestine
The pH is increased above 4 this allows the pancreatic enzymes e.g Trypsin and chymotrypsin to continue to digest the protein structure, breaking down the nutrients into absorbed matter.